Komatsu PC200-8M0, Shop Manual

Page: 1172 / 1254

100 Air conditioner
Air conditioner unit
80-100
14
PC200, 200LC, 220, 220LC-8M0
SEN06151-00
Operation
q
Thermoprobe (1a-2) senses the refrigerant tem-
perature after it passes through the evaporator
(3).
q
After the refrigerant passes through evaporator
(3), its temperature is transferred to the refriger-
ant gas (2) in the diaphragm chamber (hatched
area) through the thermoprobe (1a-2).
q
The pressure of the refrigerant gas (2) sealed in
the diaphragm chamber (hatched area) changes
in response to the temperature change of the
thermoprobe (1a-2), which therefore changes
the force (Fg) pushing the needle valve (1a).
q
The opening level of the needle valve (1a) is de-
termined based on the balance between the re-
action force exerted by the spring (1b) in a
rightward direction, and the force (Fg) of the re-
frigerant gas (2) pushing the needle valve (1a)
through the diaphragm (1a-1) in a leftward direc-
tion.
q
The refrigerant flow rate flowing from the receiv-
er drier to evaporator (3) is determined based on
the opening level of needle valve (1a).
When evaporator (3) outlet temperature is high:
[When not cooled yet: Condition (A) in the fig-
ure]
q
The pressure of the refrigerant gas (2) in the di-
aphragm chamber is high and the volume is in-
creased.
q
The force (Fg) of the refrigerant gas (2) pushing
the needle valve (1a) is increased, and the nee-
dle valve (1a) moves leftward.
q
As a result, the opening level of the needle valve
(1a) is increased and the refrigerant flow rate to
the evaporator (3) is increased to improve cool-
ing capacity.
When evaporator (3) outlet temperature is low:
[When cooled already: Condition (B) in the fig-
ure]
q
The pressure of the refrigerant gas (2) in the di-
aphragm chamber is low and the volume is de-
creased.
q
The force (Fg) of the refrigerant gas (2) pushing
the needle valve (1a) is reduced, and the needle
valve (1a) is moved rightward by the spring force
(1b).
q
The opening level of the needle valve (1a) is re-
duced and the refrigerant flow rate to the evapo-
rator (3) is reduced to lower the cooling capacity.
Dual pressure switch
a
The dual pressure switch is mounted on the air
conditioner hose under the floor.
q
The dual pressure switch turns "OFF" when the
refrigerant circuit pressure becomes abnormally
low or abnormally high.
q
When the dual pressure switch turns "OFF", the
air conditioner controller turns the compressor
clutch relay "OFF". As a result, the compressor's
magnet clutch is released and air conditioner
components are protected.
Function
a
LA or lower: Abnormally low pressure
a
HA or higher: Abnormally high pressure
LA: 0.20 MPa {2 kg/cm
2
}
LB: 0.02 MPa {0.2 kg/cm
2
}
HA: 3.14 MPa {32 kg/cm
2
}
HB: 0.59 MPa {6 kg/cm
2
}